Burghers of Calais is probably my favorite sculpture. There are only 12 castings of the Burghers, and I've seen 5 of them. Though, inexplicably, the sixth, and now most accessible of the remaining castings, in the Brooklyn Museum, is one that I continue to miss in my forays onto Long Island. I just never think of museums and Brooklyn, apparently.
I was blown away by The Gates of Hell. I saw the one in the Musee Rodin and the other that's in Musee D'Orsay.